This invention relates generally to couplings for use with coiled tubing and, more specifically, to couplings and adapters for connecting composite coiled tubing to other tools or tubing.
Coiled tubing has been used successfully in the oil and gas industry for many years. The development of new technology has expanded its role in completion, workover, drilling and production applications. The vast majority of technology and applications have focused on metallic coiled tubing and a variety of connections and adapters have been developed. Connectors for coupling consecutive strings of tubing have been developed, as have connectors for attaching a variety of well service and production tools or components to coiled tubing.
Although uses for metallic coiled tubulars have significantly increased in the past twenty years, limitations are experienced on occasion with metallic tubulars, including tensile strength limitations due to string weight and corrosion susceptibility from inhospitable conditions. Technology advancements in non-metallic, composite based coiled tubing products have facilitated solutions to many of the limitations encountered with metallic coiled tubing. Composite tubing is commonly composed of a combined resinous-fibrous outer tube concentrically encompassing a plastic inner tube, with the inner tube substantially providing sealing and flow properties and the outer tube substantially providing the strength and protective properties. When manufactured, the inner tube becomes an integral part of the outer tube. As compared to steel tubulars of like size, composite tubulars tend to have lower weight, superior burst properties, improved flow coefficients and increased fatigue resistance, while steel tends to exhibit more favorable collapse, compressive and tensile properties. Thus, in certain applications, composite tubulars are a direct alternative to steel while in other applications composites are the highly preferred option.
The physical properties of composite coiled tubing pose challenges and opportunities for the development of new technology to exploit the advantages of composite tubulars. One such opportunity relates to coupling composite coiled tubing strings either consecutively, to metallic coiled tubing or to service and/or production tools. Terminals (splices or joints) for composites tubulars are different from terminals for steel tubulars.
Technological advancements in tubular connections have been introduced over the years with a variety of couplings for connecting rigid non-metallic and flexible tubing and hoses. The prior art demonstrates a diversity of compression type couplings (e.g. Schmidt U.S. Pat. No. 3,685,860; Burge U.S. Pat. No. 3,907,335; and Anderson U.S. Pat. No. 4,032,177) grapple type couplings (e.g. Sampa 4,936,618) and wedge-style or slip- type couplings (e.g. Cox U.S. Pat. No. 5,156,206). However, the prior art fails to simultaneously achieve a combination of coupling characteristics, which are preferred for use with composite coiled tubing when used in subterranean wells. For example, prior art connections fail to provide a satisfactory mechanism for attaching threaded components to composite coiled tubing without a reduction in tensile strength or loss of positive sealing ability. In addition, otherwise desirable prior art connections fail to achieve an internally flush connection. For connecting flexible or composite tubulars, the prior art often makes use of internal cylindrical nipples supporting the connection, thereby resulting in a reduction of internal diameter. Also, threaded connections with mated positive-angle bearing threads tend to unzip or progressively shear under tensile loading.
Common grapple-type connections also frequently tend to be rather bulky, having relatively large external diameters, thus restricting the range of useful applications of larger sizes of coiled tubing to relatively larger outer tubing or casing strings. In addition, grapple and slip type couplings, which have been used successfully on metallic coiled tubing, commonly rely on compressive friction engagement to provide tensile strength in the connection. However, composite tubulars typically have a relatively lower hoop stress and crush resistance compared to steel tubulars. Therefore, grapple and slip type couplings do not provide adequate tensile strength when used with composite tubing. It is desirable, therefore, to have an improved coupling for use with composite coiled tubing to connect the tubing to other composite tubing or to metallic components without a reduction in internal diameter and with a joint efficiency exceeding 100% of the tensile strength of the tube body, while maintaining a leak-free, positive seal.
In order for tubing to be commonly accepted by operators for use as production tubing, it is highly desirable to provide a full ID joint in order to minimize pressure drops and facilitate unrestricted passage of the largest possible OD tools through the tubing. Not only will it normally be necessary to join lengths of tubing (splices), but also the tubing will have to be joined to various downhole completion tools and instruments which will be run in production wells, including, for example, landing nipples, safety valves, packers, instrumentation telemetry packages and items related to xe2x80x9csmartxe2x80x9d well completions.
A typical system for a coiled tubing operation involves a rather long length of coiled tubing, either steel, composite or other material, wound onto a relatively large reel. This invention pertains primarily to composite, plastic or resinous-based coiled tubulars. Typically, the tubing is fitted with a tool or instrument on the extended end, which is then mechanically deployed and/or retracted down a wellbore for either permanent or temporary application by winding the coiled tubing reel. Most applications necessitate coupling tools or consecutive strings of tubing together to effect the desired operations.
The present invention provides a coupling and method for connecting composite coiled tubing and affords solutions to some of the challenges of coupling composite coiled tubing to either another string of tubing or any other connection. This invention offers advantages over the prior art in that it better exploits composite coiled tubing""s advantages by offering a coupling which may have a high tensile holding strength and a full-bore, unrestricted, internal flush joint connection with a relatively small external upset coupling. The coupling may provide tensile strength and pressure rating properties equal to those properties of the coiled tubing body. The coupling may fully protect the tip-end of the composite tubing and in provides a fluid tight seal with the coiled tubing. In addition, the coupling is relatively simple in design and operation. The coupling may be applied in the field using common hand tools and conventional tools to effect the proper taper on the tubing.
One primary object of this invention is to provide a coupling that offers a joint efficiency equal to or greater than the coiled tubing body such that the coupling is not the limiting component of tensile strength. Two embodiments are disclosed in detail which afford this characteristic. The first embodiment preferably utilizes a specially designed thread profile in the threaded female adapter, which provides full body strength in the joint. A second embodiment bonds the coiled tubing to an unthreaded female adapter.
In the first embodiment, the female adapter may be comprised of a generally cylindrical, metallic coupling with two sets of inner threads; one for engaging the composite coiled tubing and one for engaging a male adapter or other male connecting component. Threads for engaging the coiled tubing preferably have a negative flank with a load-bearing angle that encourages deeper engagement into the outer layer of composite material with an increase in tension. The threads taper radially inward along the center axis of the adapter, running toward the axial midpoint of the adapter. The external surface of a composite coiled tubing string may be trimmed with a matching taper, but need not be threaded. When the coupling is threaded onto the tubing, the smooth, tapered, male end of the tubing engages the tapered threads of the female adapter. Additionally, the female adapter preferably extends axially along a portion of the external, non-tapered coiled tubing body to provide support to the connection.
The conical taper of the threads on the female adapter for engagement with the coiled tubing creates substantially even loading along the threaded engagement. These threads in the female adapter are preferably shaped with a negative bearing flank, which, unlike neutral or positive flank, do not tend to xe2x80x9cunzipxe2x80x9d as tensile forces increase. As tensile force increases, the tapered thread profile with the negative flank, which is engaged with the external surface of the coiled tubing, tends to further imbed into the non-threaded, external, tapered surface of the composite coiled tubing. Tensile loads generate substantially only shearing forces on the thread, which can be easily calculated. An advantage of this connection is that the connection does not depend upon the hoop stress of the tubing for holding strength and therefore does not require an inner nipple to support the gripping surface of the coiled tubing.
A second embodiment of a coiled tubing coupling involves bonding the coiled tubing to the female adapter. In this embodiment, the internal, negative flank threads of the female adapter may be replaced with a smooth, non-threaded, conical surface. The internal surface of the female adapter for engagement with the coiled tubing has a smooth bore, conical taper to match the external taper on the coiled tubing. A bonding agent adheres the coiled tubing to the female adapter. This method of attachment also provides tensile strength in excess of the coiled tubing body. In this embodiment, the female adapter may also extend axially along a portion of the non-tapered tubing body.
It is also an object of this invention to provide a fluid tight seal in the connection for reliably sealing with the coiled tubing. This seal may be effected by engaging a male adapter, which may be threaded, but need not be threaded, with the female adapter. The engaged end of the male adapter may have a frustoconical external surface, which may have an annular groove containing an O-ring. The composite coiled tubing may have a portion of the inner plastic liner of the coiled tubing exposed, which may protrude beyond the previously discussed portion of the coiled tubing which is threaded to the female adapter. This exposed plastic liner may be flared slightly to accept the male adapter. As the male adapter engages the female adapter, the flared plastic liner is compressed between the frustoconical surfaces of the male and female adapters. An annular groove may also be provided along the frustoconical taper of the female adapter and may also include an O-ring, thus forming a seal external to the plastic liner. In addition, a third annular groove, which may also contain an O-ring, may be included along an inside surface of the female adapter to seal the annular area between the non-tapered portion of the tubing body and the female adapter. This third O-ring redundantly seals the annular area between the female adapter and the external surface of the composite coiled tubing above the point of thread run-out and also seals the female adapter threads from a hostile well environment. In summation, the three strategically placed O-rings may provide a fluid tight seal for the connection, both internal and external to the plastic liner.
In addition to high tensile holding strength and possibly effecting a fluid tight seal, this invention also facilitates providing a flush joint connection. A cylindrical axial bore through the male adapter substantially coincides with the bore of the coiled tubing such that an internal flush jointed connection is achieved. This feature is a significant advantage over prior art coiled tubing couplings that relied upon an inner sleeve component to internally support the coupling, thereby resulting in an ID reduction in the connection.
An additional embodiment of this invention involves a modification of the male adapter to facilitate coupling two strings of coiled tubing. The male adapter may be configured into a double-male, flush joint adapter, and may be used in lieu of the previously described male adapter. The double-male adapter may generally be similar to the previously discussed male adapters connected in opposing directions with a collar which may provide a swivel connection that may be made non-rotational with a set-screw or pin. The swivel may include annular grooves containing O-rings to provide a fluid tight seal in the swivel joint. This double-male adapter facilitates coupling multiple strings of composite coiled tubing and may also preferably provide an internal flush joint connection.
The foregoing disclosure and description of the coupling and components is illustrative and explanatory thereof. This invention is not intended to be limited to the illustrated and discussed embodiments, as one skilled in the art will appreciate that various changes in the size, shape and materials, as well as in the details of the construction or combinations of features of the adapters may be made without departing from the spirit of the invention. Various embodiments exist with alternative methods of attaching the coiled tubing to the female and/or male adapter, and for attaching a male and female adapter, including, but not limited to, compression type couplings in combination with an inner sleeve, thermal bonding, chemical bonding, pinning, snap-on, ball and groove type quick-connects, mechanical-electrical connectors, friction slip and grapple type couplings.
In addition, other embodiments may utilize alternative seal arrangements such as repositioning O-rings, using packing, compression type seals, plastic bushing inserts, thread sealant compound, or any other sealing modification. Other embodiments are considered for this invention which may construct any or all of the various components out of a variety of materials, including resinous compounds, other non-metallic compounds, metallic compounds, special alloys, or any combination thereof.